1. Field of the Invention
The present invention is related to hearing systems, devices and methods. Although specific reference is made to hearing aid systems, embodiments of the present invention can be used in many applications where tissue is stimulated with at least one of vibration or an electrical current, for example with wireless communication, the treatment of neurological disorders such as Parkinson's, and cochlear implants.
People like to hear. Hearing devices can be used with communication systems and aids to help the hearing impaired. Hearing impaired subjects need hearing aids to verbally communicate with those around them. Open canal hearing aids have proven to be successful in the marketplace because of increased comfort and an improved cosmetic appearance. Another reason why open canal hearing aides can be popular is reduced occlusion of the ear canal. Occlusion can result in an unnatural, tunnel-like hearing effect which can be caused by large hearing aids which block the ear canal. However, a problem that may occur with open canal hearing aids is feedback. The feedback may result from placement of the microphone in too close proximity with the speaker or the amplified sound being too great. Thus, feedback can limit the degree of sound amplification that a hearing aid can provide. In some instances, feedback may be minimized by using non-acoustic means of stimulating the natural hearing transduction pathway, for example stimulating the tympanic membrane and/or bones of the ossicular chain. A permanent magnet or plurality of magnets may be coupled to the eardrum or the ossicles in the middle ear to stimulate the hearing pathway. These permanent magnets can be magnetically driven to cause motion in the hearing transduction pathway thereby causing neural impulses leading to the sensation of hearing. A permanent magnet may be coupled to the eardrum through the use of a fluid and surface tension, for example as described in U.S. Pat. Nos. 5,259,032 and 6,084,975.
However, work in relation to embodiments of the present invention suggests that magnetically driving the hearing transduction pathway may have limitations. The strength of the magnetic field generated to drive the attached magnet may decrease rapidly with the distance from the field generator coil to the permanent magnet. For magnets implanted to the ossicle, invasive surgery may be needed. Coupling a magnet to the eardrum may avoid the need for invasive surgery. However, there can be a need to align the driver coil with the permanent magnet, and placement of the driver coil near the magnet can cause discomfort for the user, in at least some instances.
An alternative approach is a photo-mechanical system. For example, a hearing device may use light as a medium to transmit sound signals. Such systems are described in U.S. Pat. No. 7,289,639 and U.S. Publication No. 2006/0189841. The optical output signal can be delivered to an output transducer coupled to the eardrum or the ossicle. Although optical systems may result in improved comfort for the patient, work in relation to embodiments of the present invention suggests that such systems may result in at least some distortion of the signal such that in some instances the sound perceived by the patient may be less than ideal.
Although pulse width modulation can be used to transmit an audio signal with an optical signal, work in relation to embodiments of the present invention suggests that at least some of the known pulse width modulation schemes may not work well with compact hearing devices, in at least some instances. Work in relation to embodiments of the present invention suggests that at least some of the known pulse width modulation schemes can result in noise perceived by the user in at least some instances. Further, some of the known pulse width modulation approaches may use more power than is ideal, and may rely on active circuitry and power storage to drive the transducer in at least some instances. A digital signal output can be represented by a train of digital pulses. The pulses can have a duty cycle (the ratio of active time to the overall period) that varies with the intended analog amplitude level. The pulses can be integrated to find the intended audio signal, which has an amplitude equal to the duty cycle multiplied by the pulse amplitude. When the amplitude of the intended audio signal decreases, the duty cycle can be decreased so that the amplitude of the integrated audio signal drops proportionally. Conversely, when the amplitude of the intended audio signal increases, the duty cycle can be increased so that the amplitude rises proportionally. Analog audio signals may vary positively or negatively from zero. At least some known pulse width modulation schemes may use a quiescent level, or zero audio level, represented by a 50% duty cycle. Decreases in duty cycle from this quiescent level can correspond to negative audio signal amplitude while increases in duty cycle can correspond to positive audio signal amplitude. Because this quiescent level is maintained, significant amounts of power may be consumed. While this amount of power use may not be a problem for larger signal transduction systems, it can pose problems for at least some hearing devices in at least some instances, which are preferably small and may use batteries that are infrequently replaced.
For the above reasons, it would be desirable to provide hearing systems which at least decrease, or even avoid, at least some of the above mentioned limitations of the current hearing devices. For example, there is a need to provide a comfortable hearing device with less distortion and less feedback than current devices.
2. Description of the Background Art
Patents that may be interest include: U.S. Pat. Nos. 3,585,416, 3,764,748, 5,142,186, 5,554,096, 5,624,376, 5,795,287, 5,800,336, 5,825,122, 5,857,958, 5,859,916, 5,888,187, 5,897,486, 5,913,815, 5,949,895, 6,093,144, 6,139,488, 6,174,278, 6,190,305, 6,208,445, 6,217,508, 6,222,302, 6,422,991, 6,475,134, 6,519,376, 6,626,822, 6,676,592, 6,728,024, 6,735,318, 6,900,926, 6,920,340, 7,072,475, 7,095,981, 7,239,069, 7,289,639, D512,979, and EP1845919. Patent publications of potential interest include: PCT Publication Nos. WO 03/063542, WO 2006/075175, U.S. Publication Nos. 2002/0086715, 2003/0142841, 2004/0234092, 2006/0107744, 2006/0233398, 2006/075175, 2008/0021518, and 2008/0107292. Publications and patents also of potential interest include U.S. Pat. No. 5,259,032, U.S. Pat. No. 5,276,910, U.S. Pat. No. 5,425,104, U.S. Pat. No. 5,804,109, U.S. Pat. No. 6,084,975, U.S. Pat. No. 6,554,761, U.S. Pat. No. 6,629,922, U.S. Publication Nos. 2006/0023908, 2006/0189841, 2006/0251278, and 2007/0100197. Journal publications that may be interest include: Ayatollahi et al., “Design and Modeling of Micromachines Condenser MEMS Loudspeaker using Permanent Magnet Neodymium-Iron-Boron (Nd—Fe—B)”, ISCE, Kuala Lampur, 2006; Birch et al, “Microengineered Systems for the Hearing Impaired”, IEE, London, 1996; Cheng et al., “A silicon microspeaker for hearing instruments”, J. Micromech. Microeng., 14 (2004) 859-866; Yi et al., “Piezoelectric microspeaker with compressive nitride diaphragm”, IEEE, 2006, and Zhigang Wang et al., “Preliminary Assessment of Remote Photoelectric Excitation of an Actuator for a Hearing Implant”, IEEE Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, Sep. 1-4, 2005. Other publications of interest include: Gennum GA3280 Preliminary Data Sheet, “Voyager TDTM.Open Platform DSP System for Ultra Low Power Audio Processing” and National Semiconductor LM4673 Data Sheet, “LM4673 Filterless, 2.65 W, Mono, Class D audio Power Amplifier”; and Lee et al., “The Optimal Magnetic Force For A Novel Actuator Coupled to the Tympanic Membrane: A Finite Element Analysis,” Biomedical Engineering: Applications, Basis and Communications, Vol. 19, No. 3(171-177), 2007.